Abstract. The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

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w ww ww w. .f fr ro on nt ti ie er rs si in ne ec co ol lo og gy y. .o or rg g C oastal ecosystems and the services they provide are under global siege. Climate change, nutrient loading, habitat degradation, food web alteration, and pollution all threaten their existence (Silliman et al. 2005;Orth et al. 2006;Halpern et al. 2008). Quantifying the economic values of services provided and incorporating these values into socioeconomic analyses is key to conserving these benefitgenerating ecosystems (NRC 2005;Hein et al. 2006). Currently, with few exceptions (eg Farnsworth 1998;Gaston 2000;Petersen et al. 2003;Dobson et al. 2006;Aburto-Oropeza et al. 2008), a major underlying assumption of the valuation process is that the quantity of an ecosystem function varies linearly with independent characteristics and forcing variables, such as ecosystem size, seasonality, disturbance, and species interactions (Barbier et al. 2008a). However, the responses these independent variables generate in ecosystem functions are highly dynamic and non-linear across both space and time (Farnsworth 1998). For example, the function of wave attenuation by some seagrasses may be at its maximum during summer, when plants are reproducing (Chen et al. 2007), at medium levels in spring and fall, and non-existent during winter, when density and biomass are low. Furthermore, many ecological functions are likely to be characterized by a tendency to level off (ie asymptotic relationship) or change dramatically (ie ecological thresholds) over time and space, as is the case with certain ecological processes, such as population growth, predator functional responses, and species-area relationships (Cain et al. 2008). However, such non-linear relationships between ecological traits and ecosystem function, and ecosystem function and service delivery, have not been explored in depth, quantitatively or conceptually (except see Aburto-Oropeza et al. 2008).Improvements in the understanding and quantification of non-linearities in ecosystem functions are likely to provide more realistic ecosystem service values and also to improve ecosystem-based management (EBM) practices (Barbier et al. 2008a). Current conservation decision making often takes into account only the qualitative benefits of ecosystems (eg whether or not a habitat is a fish nursery, rather than the value of the fisheries it maintains), as quantitative measures are generally unavailable.

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Biological processes in seagrass meadows are regulated by the exchange of momentum, heat and mass between the surrounding water and the plants and thus may strongly depend on the characteristics of water flow and turbulence. Comparisons of mean flow profiles, turbulence distribution and mixing in meadows of the seayrass Thalassia testudinum colonizing 2 hydrodynamically different sites (wave-dominated and tide-dominated) suggest that the hydrodynamic microclimate and consequently mixing within seagrass beds strongly depend on the hydrodynamic forces (waves and currents) acting on the plants. Unidirectional flows deflect the water over the meadow (skimming flows). which potentially leads to lower mixing between the water above and within the meadow. In contrast, waves cause the blades to move back and forth, increasing the exchange between the water column and that within the meadow. Therefore, the hydrodynamic conditions prevailing in the seagrass habitat (waves, tides) change the pattern of flow attenuation and mixing within the vegetation.

Ecosystem-based management is logistically and politically challenging because ecosystems are inherently complex and management decisions affect a multitude of groups. Coastal ecosystems, which lie at the interface between marine and terrestrial ecosystems and provide an array of ecosystem services to different groups, aptly illustrate these challenges. Successful ecosystem-based management of coastal ecosystems requires incorporating scientific information and the knowledge and views of interested parties into the decision-making process. Estimating the provision of ecosystem services under alternative management schemes offers a systematic way to incorporate biogeophysical and socioeconomic information and the views of individuals and groups in the policy and management process. Employing ecosystem services as a common language to improve the process of ecosystem-based management presents both benefits and difficulties. Benefits include a transparent method for assessing trade-offs associated with management alternatives, a common set of facts and common currency on which to base negotiations, and improved communication among groups with competing interests or differing worldviews. Yet challenges to this approach remain, including predicting how human interventions will affect ecosystems, how such changes will affect the provision of ecosystem services, and how changes in service provision will affect the welfare of different groups in society. In a case study from Puget Sound, Washington, we illustrate the potential of applying ecosystem services as a common language for ecosystem-based management.